KC Gardens

Japanese beetles are back! Here’s the good and bad news about these garden pests

Tips on how to control Japanese beetles

Horticulturist Anne Wildeboor said volunteers for the Overland Park Arboretum spend a couple hours every morning dealing with Japanese beetles. She provides some tips on how to spot and control them in your gardens.
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Horticulturist Anne Wildeboor said volunteers for the Overland Park Arboretum spend a couple hours every morning dealing with Japanese beetles. She provides some tips on how to spot and control them in your gardens.

Remember the line from the movie “Poltergeist” — “They’re back.” We can use that to refer to the ravenous Japanese beetles as they return to rain havoc on gardens.

Once a seldom seen insect, they are now well established, so expect this feeding frenzy every summer.

The adult Japanese beetle is shiny bronze-green with white dots. It feeds on over 300 plant species. They love roses, grapes and linden trees but feed on green beans, hibiscus and crepe myrtles as well.

Few garden plants are exempt from their destruction. There is good news and bad news about this.

The good news is rarely do they kill the plant. Instead, the foliar feeding causes the plant to look unsightly.

The bad news is controlling them is not easy. Many gardeners just let them have their way for the four- to six-week period they are active. Tolerance is a challenging trait to practice. Instead, many people reach for chemical controls.

Numerous products on the market are labeled for control. Reapply the product every week or two, depending on the product selected. But be aware, these insecticide applications also take their toll on beneficial insects.

The best organic option for Japanese beetle control is hand removal. While time consuming and hardly fun, it is effective.

Think of hand removal as an excellent way of taking a daily stroll through the garden. As you walk, knock the beetles into a bucket of soapy water to meet their demise.

The ideal time to take action is in the cool of the morning. They are sluggish earlier in the day and become more active as the day gets hotter.

Internet rumors caution about knocking the shiny beetles to the ground and stepping on them. It is thought that crushing them releases a pheromone that attracts more beetles. Research has found that crushing does not draw more feeders.

It is true that Japanese beetles are drawn to an area by the use of pheromones. Japanese beetle traps, or lures, are baited with the scent to attract the adults. They fall into the trap and cannot fly out. These traps are effective in attracting the beetles.

Here is the problem — they attract more beetles to your landscape than they catch. Placing a trap in your garden can actually increase feeding. If you do use a trap, put it as far away from desirable plants as possible. My advice is not to use the traps in an urban or suburban setting.

Japanese beetles also have a grub stage that can damage lawns. Luckily grub control treatments work. But controlling the grubs in your lawn will have little effect on the number of adults that feed on your plants as they fly in from surrounding areas.

When it comes to the annual appearance and feeding of this destructive pest, the best advice may be to remember the age-old saying: “This too shall pass.”

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.

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